Field of the Invention
The present invention relates to an image forming apparatus and a control method that is performed in an image forming apparatus.
Description of the Related Art
In general, in an image forming apparatus utilizing an electrophotographic process technology, laser light based on image data is applied to a charged photosensitive member to form an electrostatic latent image. Then, toner is supplied from a development device to the photosensitive member on which the electrostatic latent image is formed, and thus the electrostatic latent image is visualized to form a toner image. Furthermore, the toner image is transferred either directly or indirectly to a sheet and is then fixed by being heated and pressurized, and thus the image is formed on the sheet.
In the image forming apparatus described above, a blade or the like is brought into a sliding contact with the surface of the photosensitive member on which the toner image is formed, and thus attachments such as a residual toner attached to the surface of the photosensitive member are removed (cleaned). When the photosensitive member is cleaned with the blade or the like, in order to reduce an attachment force of the toner to the photosensitive member to enhance the cleaning performance, a technology is used in which the toner to which a lubricant is externally added is applied and the lubricant is attached to the surface of the photosensitive member.
It is known that the attached amount of lubricant on the surface of the photosensitive member greatly affects the cleaning performance. For example, when the attached amount of lubricant is decreased, since the residual toner or the like is easily attached to the surface of the photosensitive member, it becomes difficult to perform the cleaning, with the phenomenon that the toner is passed through or an edge part of the blade is drawn in the direction of movement (the direction of rotation) of the photosensitive member and is thereby turned up.
Here, the case where the attached amount of lubricant is decreased will be specifically described. The lubricant externally added to the toner has an opposite polarity (for example, a positive polarity) so as to be attached to the toner, and a large proportion of the lubricant is moved to a part (negatively charged white part) of the surface of the photosensitive member that is not exposed at the time of development.
Hence, when the image formation processing of low coverage (low print rate) is continuously performed, in a state where a small amount of toner is supplied to the development device, a large amount of lubricant is moved from the development device to the photosensitive member as compared with the toner, with the result that the lubricant in the development device may be exhausted. When the lubricant in the development device is exhausted, the lubricant to be attached to the photosensitive member runs out, and thus the amount of lubricant on the photosensitive member is gradually lowered, with the result that the phenomenon described above occurs.
Therefore, when the image formation processing of low coverage is performed, a low production-time forced discharge toner image (toner image by toner refresh patch control; in the present application, also referred to as the “RFP”) is formed in a non-image formation region of the photosensitive member such that the toner to which the lubricant is externally added is newly supplied to the development device. In many cases, the RFP is a belt-shaped toner image.
The RFP is formed, and thus it is possible to avoid a possibility that the lubricant in the development device is exhausted and hence a possibility that the amount of lubricant on the photosensitive member is lowered. The non-image formation region of the photosensitive member refers to a region between image formation regions each formed by a toner image transferred to one sheet of paper, and generally refers to a “region between sheets”.
Japanese Unexamined Patent Application Publication No. 2000-206744 discloses an image forming apparatus that prevents image quality defects such as inconsistencies in image density and fogging. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2000-206744, before formation of an electrostatic latent image, the image density of an image formed on an image carrying member is detected, and when the detection value is determined to be lower than a desired value, a predetermined electrostatic latent image is formed to forcefully consume a developer in a development device.
Japanese Unexamined Patent Application Publication No. 2003-76079 discloses an image forming apparatus that removes a failure caused by the degradation of a developer when a development device is driven in a state where a small amount of toner is consumed. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-76079, the area ratio of an image formed and the development drive time of a development device are detected, and a developer is forcefully consumed according to the image area ratio per unit drive time of the development.
Japanese Unexamined Patent Application Publication No. 2005-43388 discloses a technology that prevents failures such as the lowering of image quality caused by the fatigue/degradation of a developer. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-43388, an image area ratio per unit movement distance of a developer carrying member is detected, and based on the result of the detection, the forced consumption of toner is controlled.
When the region between sheets is prolonged to some degree such as by a post-processing machine operation, the wait of insert paper or the wait of a machine on one side in a series tandem, the photosensitive member is idled therebetween, and the lubricant is supplied from the development device to the photosensitive member in a state where an extremely small amount of toner is supplied. Hence, in such a case, after the start of the drawing of the RFP (low production-time forced discharge toner image) (the formation of the first RFP), for example, the RFP is periodically formed.
Here, consideration will be given to timing at which the RFP is drawn. Since under conditions in which the image formation processing of low coverage has been performed, it is assumed that the lubricant in the development device has already been reduced considerably, it is preferable to draw the RFP earlier.
However, under conditions in which the image formation processing of high coverage has been performed, as compared with the conditions in which the image formation processing of low coverage has been performed, it is assumed that the lubricant is less reduced, and even if the RFP is drawn relatively late, it is possible to maintain the appropriate application of the lubricant to the photosensitive member. As described above, the RFP is drawn late, and thus the consumed amount of toner is reduced accordingly.
In view of the foregoing conditions, the present invention has an object to provide an image forming apparatus and a control method that can achieve both a reduction in the consumed amount of toner and the appropriate application of the lubricant to the photosensitive member.